I found this great website through work, because we buy labels in bulk, but apparently, for people planning large events, or whatever you can use Dollar Tree Direct a website the store Dollar Tree recently started up , where you can buy anything you see in a store, in bulk. I think this service is fairly new. Here is a write-up from the press release on Retail Net.
Dollar Tree has launched an e-commerce site called "Dollar Tree Direct" (www.dollartreedirect.com) designed for customers who want to purchase large quantities of items from the store.Customers can submit orders via electronic submission, fax or by phone. No matter what method they choose, shoppers will have the chance to speak with a customer-service representative who will check on availability of requested items and process payments.
It doesn't look like a whole lot that I've seen in the stores is on the web site yet, but as long as you have the product number you can call-in an order.